In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. One defect in prior formation techniques is caused when an air bubble is trapped between the forming roller and the polyethylene which will form the surface for casting of photosensitive materials. This air bubble will form a pit that will cause a defect in the photographic performance of photographic materials formed on the polyethylene. It would be desirable if a more reliable and improved surface could be formed at less expense.
In color papers there is a need for providing color papers with improved resistance to curl. Present color papers will curl during development and storage. Such curl is thought to be caused by the different properties of the layers of the color paper as it is subjected to the developing and drying processes. Humidity changes during storage of color photographs lead to curling. There are particular problems with color papers when they are subjected to extended high humidity storage such as at greater than 50% relative humidity. Extremely low humidity of less than 20% relative humidity also will cause photographic papers to curl.
In photographic papers the polyethylene layer also serves as a carrier layer for titanium dioxide and other whitener materials as well as tint materials. It would be desirable if the colorant materials rather than being dispersed throughout the polyethylene layer could be concentrated nearer the surface of the layer where they would be more effective photographically.
It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene in receiver sheets for thermal dye transfer.
It would be desirable if paper base materials could be made smoother. In conventional practice paper base materials are coated with a layer of polyethylene which serves as the base for imaging layers. The method of casting of the polyethylene onto the paper base results in imperfections in the surface onto which the imaging layers are cast. These imperfections are at least the result of the roughness of the paper base material. The paper base has a particularly objectionable roughness in the spatial frequency range of 0.3 to 6.35 mm. This results in a defect usually referred to as orange peel. It would be desirable if this defect in photographic base paper could be minimized or eliminated.
Problem to be Solved by the Invention
There remains a need for photographic papers that have less surface roughness so that the photographic images are glossier and smoother.